Wireline operations are carried out in oil and gas wells on a regular basis. Wireline is used to convey a toolstring down hole to perform setting or retrieving tasks. A wireline toolstring comprises a combination of different pieces of equipment screwed together to form a working unit. This unit is manipulated from the surface via the wireline which can be made to perform either upward or downward jarring by either reeling in or reeling out wire from the winch.
Pressure control equipment is attached to the well-head which will include a "stuffing box" and a "blow-out preventer". This equipment is used to seal against the wire while running into or out of the hole, and to seal against the wire in emergency situations respectively.
The wire is attached to the toolstring by means of a "rope socket" which is essentially a wire clamp.
Situations occur from time to time when the toolstring becomes stuck downhole. When this happens the only way to recover the wire from the well is by attaching at the surface a "cutter tool" which will slide down the wire, cutting on impact at the rope socket. Time is lost when attaching this cutter tool as the blow out preventer has to be sealed across the wire to hold back well pressure while the tool is attached to the wire. Another disadvantage is that the cutter tool may cut the wire prematurely if it hits a restriction on its way downhole.